Monday, February 11, 2013

An early phylogenetic classification (1884)

The history of phylogenetics has concentrated on those people who made (ostensibly) original contributions to theory, with very little mention of those who synthesized empirical information. A prominent member of the latter group was the marine zoologist William Abbott Herdman (1858–1924), who was Derby Professor of Natural History at University College, Liverpool (1881–1919) and then Professor of Oceanography (1919–1920).

At the Fourth Ordinary Meeting (December 1, 1884) of the 74th Session (1884–1885) of the Literary and Philosophical Society of Liverpool he presented a paper entitled "A phylogenetic arrangement of animals". The Society duly published this the next year (Herdman W.A. 1885. A phylogenetic arrangement of animals. Proceedings of the Literary and Philosophical Society of Liverpool 39: 65-85). This publication contained an explicitly phylogenetic tree and an accompanying classification reflecting that tree (which the author calls a "natural classification").

At the same time, Herdman published a book (Herdman W.A. 1885. A Phylogenetic Classification of Animals (For the Use of Students). Macmillan, London; Adam Holden, Liverpool) with this prefaratory note:

The accompanying Genealogical Table was drawn up in May, 1884, mainly from various partial schemes of classification which I have been in the habit of using in my lectures for several years; and a brief description was read in the following December before the Literary and Philosophical Society of Liverpool. While preparing this paper for publication it occurred to me that in an extended form it might prove serviceable to students of Biology: hence its issue in the present condition.

This book is available at the Open Library, and the above illustration (which Herdman calls a "table") is taken from it. It appears to be the same as the one in the journal publication; and the text of the book (76 pp) is, indeed, an expanded version of that in the paper. (The book apparently was published first.)

The tree has much in common with modern phylogenetic trees, in that Herdman emphasizes single common ancestors, and all contemporary taxa are on side-branches, but it differs in having a strong central axis, and in trying to represent "relative advancement" (ie. Herdman recognizes grades as well as clades). For example, in the Explanatory notes accompanying the diagram, he explains:

The lowest organisms are placed at the foot of the Table, the highest at the top. The line, straight or zig-zag, traced from the very base upwards to any name indicates the probable course of the evolution of the group of animals to which the name belongs. If a line stretches upwards it shows an advance in structure; if it is nearly horizontal it means that little or no upward evolution has taken place; if it slopes downwards, that indicates degeneration or degradation. The proportional lengths and angles of the various lines are meant to represent roughly the amount and the nature of the evolution which has taken place.

In no case has the line representing the evolution of one group been allowed to pass through another group. All existing animals are represented as being at the ends of lines or branches.

It is scarcely necessary to point out that horizontal lines could not be drawn across this table in such a way as to divide it into sections representing the Fauna of the various geological periods. In order to show that, a very different table would require to be constructed in which distance along a line stretching upwards from the base would indicate merely the age of the group and not evolution or advance in organisation as in the present table.

What is of most interest here is the sole reticulation shown in the tree, which involves the Gregarinida (now part of the phylum Apicomplexa). Herdman's description of this is (pp 7-8):

The Gregarinida, like all parasitic organisms, are difficult to place, as there is always a probability that they have been considerably modified, or even degraded from the ancestral type, in consequence of their habits. They are placed in the table at the end of a long branch springing from the main stem of the Protozoa, close to the highest Monera, and extending outward and upward so as to reach a point a little above the level of Amoeba, but far from the axis. The length of the line shows the considerable amount of differentiation attained by the group and its somewhat isolated position, while its point of origin indicates the relationship which probably exists with the Monera, There is a similarity with the life-history of Myxastrum, and the ancestors of the Gregarinida may have diverged from the other Protozoa at a point close to this form, or one of the other allied Monera. On the other hand, it is possible that the Gregarinida may have degenerated from one of the higher Protozoa — from some form above Amoeba — or even from still higher animals. The dotted line in the table, stretching downwards from the base of the Metazoa, may serve to recall the possibility that the Gregarinida are a much degraded offshoot from some group of Gastrea-like organisms.

So, in this case the reticulation represents ambiguity regarding the evolutionary history. This is unusual for its time; and indeed this may be the first occasion on which a phylogenetic reticulation was used to represent anything other than hybridization. (It is not the first time that anyone presented conflicting evolutionary histories, however: Is this the first network from conflicting datasets?)

Finally, Herdman explicitly states his intention to provide a synthesis of contemporary empirical knowledge. This is also notable, given that many of his contemporaries were still doubtful about the feasibility of deriving an empirically based phylogenetic tree. Herdman notes in his Preface:

It is obvious that a classification such as this can only be in a limited sense original. It must of necessity agree in many respects with older schemes, amongst which the well-known diagrams of Professor Haeckel, published first in 1866, are the most notable of those in a tree-like form.

In working out the details of the table many books have been consulted, and I have tried to incorporate the views of the latest authorities so far as they commended themselves to my judgment. I may expressly mention the extensive use that has been made of various books and papers by Huxley, Ray Lankester, Moseley, Haeckel, Glaus, and others; and particularly of that invaluable work, Balfour's Treatise on Comparative Embryology.

Herdman himself was interested in marine zoology, oceanography and geology. He is perhaps best known for his role in The Liverpool Marine Biology Committee (1885–1919). The Committee established a small biological station on Puffin Island, off the North coast of Anglesey, in 1887; and in 1892 a new, larger and better equipped station was opened at Port Erin, near the southern tip of the Isle of Man. (See S.J.H. 1920. The Liverpool Marine Biology Committee. Nature 104: 677.)

Indeed, Alfred Rosenberger's chapter in Ecology and Behavior of Neotropical Primates (1981) states: "E. Ceoffroy (1812) had identified the three major suprageneric groupings that are still considered to be basic classificatory units. Ceoffroy recognized the Arctopitheci, comprised exclusively of the clawed, two-molared marmosets; the Helopitheci, including the larger species having prehensile tails, Cebus,Alouatta and the spider-woollys; and the Geopitheci, embracing the remaining platyrrhines and typified by their lack of a prehensile tail and their retention of three molar teeth."